A SPAD is based on a p-n junction device biased beyond its breakdown region. The high reverse bias voltage generates a large enough electric field such that a single charge carrier introduced into the depletion layer of the device can cause a self-sustaining avalanche via impact ionization. The avalanche is quenched, either actively or passively to allow the device to be “reset” to detect further photons. The initiating charge carrier can be photo-electrically generated by a single incident photon striking the high field region. It is this feature which gives rise to the name “Single Photon Avalanche Diode.” This single photon detection mode of operation is often referred to as Geiger Mode.
U.S. Pat. No. 7,262,402 to Niclass et al. discloses an imaging device using an array of SPADs for capturing a depth and intensity map of a scene, when the scene is illuminated by an optical pulse. U.S. Patent Application No. 2007/0182949 to Niclass discloses an arrangement for measuring the distance to an object. The arrangement uses a modulated photonic wave to illuminate the object and an array of SPADs to detect the reflected wave. Various methods of analysis are disclosed to reduce the effects of interference in the reflected wave.
Navigation devices, such as scroll wheels and mice, are used in many applications, including phones, computers, and many other devices or systems. A typical mouse scroll wheel provides motion control in either one or two axes and can be used to move a cursor up and down a screen and/or tilted to left and right. Similarly, a mouse, such as a fingermouse, may be used in many environments. A fingermouse can also detect movement in two axes, thereby providing four degrees of freedom. The fingermouse also may be used to move a cursor up and down and left and right on a screen.